Diabetes refers to a disease process derived from multiple causative factors and characterized by elevated levels of plasma glucose or hyperglycemia. Uncontrolled hyperglycemia is associated with increased and premature mortality due to an increased risk for microvascular and macrovascular diseases, including nephropathy, neuropathy, retinopathy, hypertension, stroke, and heart disease. Therefore, control of glucose homeostasis is critically important approach for the treatment of diabetes.
There are two generally recognized forms of diabetes. In type I diabetes, or insulin-dependent diabetes mellitus (IDDM), patients produce little or no insulin, the hormone which regulates glucose utilization. In type II diabetes, or noninsulin dependent diabetes mellitus (NIDDM), patients often have plasma insulin levels that are the same or even elevated compared to nondiabetic humans; however, these patients have developed a resistance to the insulin stimulating effect on glucose and lipid metabolism in the main insulin-sensitive tissues, muscle, liver and adipose tissue and the plasma insulin levels are insufficient to overcome the pronounced insulin resistance.
Insulin resistance is not primarily due to a diminished number of insulin receptors but to a post-insulin receptor binding defect that is not yet understood. This resistance to insulin responsiveness results in insufficient insulin activation of glucose uptake, oxidation and storage in muscle and inadequate insulin repression of lipolysis in adipose tissue and of glucose production and secretion in liver.
The common treatments for NIDDM, which have not changed substantially in many years, are all with limitations. While physical exercise and reductions in dietary intake of calories will dramatically improve the diabetic condition, compliance with this treatment is very poor because of well-entrenched sedentary lifestyles and excess food consumption, especially of high fat-containing food. Increasing the plasma level of insulin by administration of sulfonylureas (e.g. tolbutamide, glipizide) which stimulate the pancreatic .beta.-cells to secrete more insulin or by injection of insulin after the response to sulfonylureas fails will result in high enough insulin concentrations to stimulate the very insulin-resistant tissues. However, dangerously low levels of plasma glucose can result from these last two treatments and increasing insulin resistance due to the even higher plasma insulin levels could occur. The biguanides increase insulin sensitivity resulting in some correction of hyperglycemia. However, the two biguanides, phenformin and metformin, can induce lactic acidosis and nausea/diarrhea, respectively.
The glitazones (i.e. 5-benzylthiazolidine-2,4-diones) are a more recently described class of compounds with potential for a novel mode of action in ameliorating many symptoms of NIDDM. These agents substantially increase insulin sensitivity in muscle, liver and adipose tissue in several animal models of NIDDM resulting in complete correction of the elevated plasma levels of glucose, triglycerides and nonesterified fatty acids without occurrence of hypoglycemia.
Hyperlipidemia is a condition which is characterized by an abnormal increase in serum lipids, such as cholesterol, triglycerides and phospholipids. These lipids do not circulate freely in solution in plasma, but are bound to proteins and transported as macromolecular complexes called lipoproteins. See the Merck Manual, 16th Ed. 1992 (see for example pp. 1039-1040) and "Structure and Metabolism of Plasma Lipoproteins" in Metabolic Basis of Inherited Disease, 6th Ed. 1989, pp. 1129-1138.
One form of hyperlipidemia is hypercholesterolemia, characterized by the existence of elevated LDL cholesterol levels. The initial treatment for hypercholesterolemia is often to modify the diet to one low in fat and cholesterol, coupled with appropriate physical exercise, followed by drug therapy when LDL-lowering goals are not met by diet and exercise alone. LDL is commonly known as the "bad" cholesterol, while HDL is the "good" cholesterol. Although it is desirable to lower elevated levels of LDL cholesterol, it is also desirable to increase levels of HDL cholesterol. Generally, it has been found that increased levels of HDL are associated with lower risk for coronary heart disease (CHD). See, for example, Gordon, et al., Am. J. Med., 62, 707-714 (1977); Stampfer, et al., N. England J. Med., 325, 373-381 (1991); and Kannel, et al., Ann. Internal Med., 90, 85-91 (1979). An example of an HDL raising agent is nicotinic acid, but the quantities needed to achieve HDL raising are associated with undesirable effects, such as flushing.
Peroxisome proliferators are a structurally diverse group of compounds that when administered to rodents elicit dramatic increases in the size and number of hepatic and renal peroxisomes, as well as concomitant increases in the capacity of peroxisomes to metabolize fatty acids via increased expression of the enzymes of the beta-oxidation cycle. Compounds of this group include but are not limited to the fibrate class of hyperlipidemic drugs, herbicides and phthalate plasticizers. Peroxisome proliferation is also triggered by dietary or physiological factors such as a high-fat diet and cold acclimatization.
Three sub-types of peroxisome proliferator activated receptor (PPAR) have been discovered and described; they are peroxisome proliferator activated receptor alpha (PPAR.alpha.), peroxisome proliferator activated receptor gamma (PPAR.gamma.) and peroxisome proliferator activated receptor delta (PPAR.delta.). Identification of PPAR.alpha., a member of the nuclear hormone receptor superfamily activated by peroxisome proliferators, has facilitated analysis of the mechanism by which peroxisome proliferators exert their pleiotropic effects. PPAR.alpha. is activated by a number of medium and long-chain fatty acids, and it is involved in stimulating .beta.-oxidation of fatty acids. PPAR.alpha. is also involved with the activity of fibrates and fatty acids in rodents and humans. Fibric acid derivatives such as clofibrate, fenofibrate, bezafibrate, ciprofibrate, beclofibrate and etofibrate, as well as gemfibrozil, produce a substantial reduction in plasma triglycerides along with moderate reduction in LDL cholesterol, and they are used particularly for the treatment of hypertriglyceridemia.
The PPAR.gamma. receptor subtypes are involved in activating the program of adipocyte differentiation and are not involved in stimulating peroxisome proliferation in the liver. There are two isoforms of PPAR.gamma.: PPAR.gamma.1 and PPAR.gamma.2, which differ only in that PPAR.gamma.2 contains an additional 28 amino acids present at the amino terminus. The DNA sequences for the isotypes are described in Elbrecht, et al., BBRC 224;431-437 (1996). In mice, PPAR.gamma.2 is expressed specifically in fat cells. Tontonoz et al., Cell 79: 1147-1156 (1994) provide evidence to show that one physiological role of PPAR.gamma.2 is to induce adipocyte differentiation. As with other members of the nuclear hormone receptor superfamily, PPAR.gamma.2 regulates the expression of genes through interaction with other proteins and binding to hormone response elements for example in the 5' flanking regions of responsive genes. An example of a PPAR.gamma.2 responsive gene is the tissue-specific adipocyte P2 gene. Although peroxisome proliferators, including the fibrates and fatty acids, activate the transcriptional activity of PPAR's, only prostaglandin J.sub.2 derivatives have been identified as natural ligands of the PPAR.gamma. subtype, which also binds thiazolidinedione antidiabetic agents with high affinity.
The human nuclear receptor gene PPAR.delta. (hPPAR.delta.) has been cloned from a human osteosarcoma cell cDNA library and is fully described in A. Schmidt et al., Molecular Endocrinology, 6 :1634-1641 (1992), herein incorporated by reference. It should be noted that PPAR.delta. is also referred to in the literature as PPAR.beta. and as NUC1, and each of these names refers to the same receptor; in Schmidt et al. the receptor is referred to as NUC1.
In WO96/01430, a human PPAR subtype, hNUC1B, is disclosed. The amino acid sequence of hNUC1B differs from human PPAR.delta. (referred to therein as hNUC1) by one amino acid, i.e., alanine at position 292. Based on in vivo experiments described therein, the authors suggest that hNUC1B protein represses hPPARa and thyroid hormone receptor protein activity.
It has been disclosed in WO97/28149 that agonists of PPAR.delta. are useful in raising HDL plasma levels. WO97/27857, 97/28115, 97/28137 and 97/27847 disclose compounds that are useful as antidiabetic, antiobesity, anti-atherosclerosis and antihyperlipidemic agents, and which may exert their effect through activation of PPARs.
It has been suggested that glitazones exert their effects by binding to the peroxisome proliferator activated receptor (PPAR) family of receptors, controlling certain transcription elements having to do with the biological entities listed above. See Hulin et al., Current Pharm. Design (1996) 2, 85-102. The glitazones have been shown to bind exclusively to the PPAR.gamma. subtype.
All the glitazones that have progressed to clinical trials in human, and almost all of the glitazones that have been reported in the literature have the molecular motif of an aryl group attached to the 5-position of thiazolidinedione via a one carbon spacer. Although several compounds having a 4-(oxy)phenyl group directly attached to the 5-position of thiazolidinedione have been prepared and tested as potential antidiabetic agents, they have been stated to lack hypoglycemic activity.
Thus, the compound 5-[4-[2-(2-benzoxazolylmethylamino) ethoxy]phenyl]-2,4-thiazolidinedione (1) showed no antihyperglycemic activity in ob/ob mice, and subsequent studies showed this compound to require relatively high amounts for PPAR.gamma. activation. (Cantello et al, J. Med. Chem., 1994, 37:3977-3985 and Willson et al, J. Med. Chem., 1996, 39:665-668). ##STR1##
The compound 5-[4-(phenylethoxy)phenyl]-2,4-thiazolidinedione (2) showed no antihyperglycemic effect in diabetic mouse model, even though it may have aldose reductase inhibitory activity. (Sohda et al, Chem. Pharm. Bull., 1982, 30:3580-3600, and Sohda et al, Chem. Pharm. Bull., 1982, 30:3601-3616). Examples of other phenylthiazolidinedione aldose reductase inhibitors include 5-[4-(4-chlorophenoxy)phenyl]-2,4-thiazolidinedione, 5-[4-(4-chlorobenzyloxy)phenyl)-2,4-thiazolidinedione, 5-[4-(2-pyridylethoxy)phenyl]-2,4-thiazolidinedione, 5-[4-(6-methyl-2-pyridylethoxy)phenyl]-2,4-thiazolidinedione, and 5-[4-(2-thienylethoxy)phenyl]-2,4-thiazolidinedione. (Sohda et al, Chem. Pharm. Bull., 1982, 30:3601-3616). ##STR2##
PCT Published Application WO97/22600 discloses antihyperglycemic 5-[3-(carboxamido)phenyl]-2,4-thiazolidinediones of the formula ##STR3##
The present inventors have found that certain substituted 5-aryl-2,4-thiazolidinediones are potent agonists of PPAR, in particular the .alpha., .delta. and/or .gamma. subtypes, and especially the .gamma. subtype including dual agonists of the .alpha./.gamma. subtypes. These compounds are therefore useful in the treatment, control or prevention of diabetes, hyperglycemia, hyperlipidemia (including hypercholesterolemia and hypertriglyceridemia), atherosclerosis, obesity, vascular restenosis, and other PPAR .alpha., .delta. and/or .gamma. mediated diseases, disorders and conditions.